Method of constructing a prestressed concrete circular wall

ABSTRACT

A procedure for constructing circular walls in sectors, including pre-stressing peripheral reinforcing rods in each sector as segments in a continuous peripheral tension system, and including provision for grouting the pre-stressed rods through the use of hollow rods and vented couplings.

llnite '1 Williams States Patent [1 1 [451 Mar. 4, 1975 METHOD OF CONSTRUCTING A PRESTRESSED CONCRETE CIRCULAR WALL [76] Inventor: Chester 1. Williams, 1501 Madison S.E.. Grand Rapids, Mich. 49507 1 Filed: Feb. 19, 1974 [21] Appl. N0.: 443,828

[52] U.S. C1 264/33, 52/224, 52/248, 52/583, 264/228. 52/741 [51] Int. Cl. 1304b 1/16, E040 5/07 [58] Field of Search 52/741, 744, 224, 223, 52/225-238, 192, 193. 245, 248, 583; 264/33, 228

[56] References Cited UNITED STATES PATENTS 1.834.842 12/1931 Houghtaling 52/583 2.185.749 1/1940 Kennedy 52/248 3.022.713 2/1962 Friberg 264/228 3.089.215 5/1963 Stubbs 3.604.038 2/1972 Heron 52/248 FOREIGN PATENTS OR APPLlCATlONS 155,756 3/1954 Australia 52/223 1,526,601 4/1968 France 52/583 522.510 11/1928 Germany 52/223 Primary E.\'uminer-Frank L. Abbott Assistant Exuminer-James L. Ridgill. Jr. Attorner, Agent, or FirmGlenn B. Morse [57] ABSTRACT A procedure for constructing circular walls in sectors. including pre-stressing peripheral reinforcing rods in each sector as segments in a continuous peripheral tension system, and including provision for grouting the pre-stressed rods through the use of hollow rods and vented couplings.

7 Claims, 9 Drawing Figures PATENIEDM 41915 3.869.530 snmes q 54 V 3 Fig. 4 40 60 6| 56 64 47 l I I PATENTED .41975 suwsggg IIIIIIIII IIIIIIII PATENTED 3.869.530 saw u g g METHOD OF CONSTRUCTING A PRESTRESSED CONCRETE CIRCULAR WALL BACKGROUND OF THE INVENTION It is standard practice to construct poured concrete walls through the use of spaced form sections interconnected by ties of sufficient strength to resist the pressure of the poured concrete. The form sections are usually metal or plywood panels reinforced by parallel stiffening beams commonly referred to as studs. Another set of beams. usually referred to as walers" extends transversely to the studs, and bears against them to transfer the accumulated stresses to the tie assemblies. These tie assemblies usually include a central tie rod that remains imbedded in the concrete, and has threaded ends inter-engaged with bolts extending to an adjustable member bearing against the walers. The bolts traverse holes in the form panels, and these assemblies are usually identical with each ofthe form sections. The tie systems are frequently used additionally to control the spacing of the forms. When the concrete is poured in the space between the form panels, and is permitted to set, the result is a concrete wall with dimensions that are controlled by the accuracy of placement of the form system. This standard construction procedure is used for walls that are both linear and curved in plan, and with or without reinforcement.

The reinforcement of concrete walls and other structures is normally accomplished through the use of steel bars having a corrugated surface for maximum interengagement between the rods and the surrounding concrete. Concrete is very strong in compression, but notoriously unreliable in tension. The placement of reinforcing rods is usually selected so that the rods can take over the function of providing strength in tension. Since material cannot develop tensile stress without elongation, it is preferable that the reinforcing rods be pre-stressed so that the concrete is not required to stretch before the imbedded rods can develop tensile strength. This obviously dictates that the pre-stress must be applied before the concrete is poured, unless special provision is made to prevent bonding of the concrete to the reinforcing rods. So-called posttensioning involves the application of prestress tension to the rods through the use of hydraulic jacks, or other force-generating equipment. Performing this op cration prior to pouring the concrete obviously requires that prc-strcss forces be transmitted through the form system. which is ordinarily impractical in the field. While the isolation of reinforcing rods from surrounding concrete has been accomplished by surrounding the rod with a shielding tube or coating, this principle has not been effectively applied to the construction of pre-stressed successive wall sectors, to applicants knowledge.

Wherever reinforcing rods are used, it is usually considered advisable to assure that they are ultimately imbedded in a cementitious material, which can either be concrete or an initially more flowable material referred to as grout. The intimate engagement of the reinforcing rods by grout or concrete protects the rods from the effects of moisture or other corrosive influences, as well as providing some degree of stress transfer where this is not interfered with by a shielding material. In any event, it is always desirable to eliminate any voids that may exist in a concrete structure. Standard procedures in the construction of concrete walls do not conveniently provide the features of pre-stress and groutability, particularly where the walls are circular in plan.

SUMMARY OF THE INVENTION Walls forming an enclosure that are curved in plan are constructed by placing shielded reinforcing rods in the space between the form sections so that the rods extend peripherally. The wall is constructed in sectors. with each rod unit extending generally along the axis of the sector, and projecting from the end or ends of the form system that confines the poured concrete for that particular sector. The reinforcing rods are preferably positioned by the tie system securing the form sections. When the concrete is poured and is permitted to set, the reinforcing rods (which have been prevented from bonding to the surrounding concrete) may be posttensioned to the desired degree of pre-stress. The tensioning forces are applied to the portions of the rods extending from the cast concrete. Each successive wall sector is constructed in a similar fashion. Its reinforcing rod is coupled to the projecting threaded end of the reinforcing rod of the previously-cast sector. Posttensioning is then applied to the opposite end ofthe rod after the concrete of the new sector has set. The tensioning is preferably generated by the use of hydraulic jack acting against the end of the cast concrete, and a nut is run down onto a bearing plate after the tension forces have been generated. The construction of the closure sector is slightly different, in that the projecting end of the last reinforcing rod is connected to the threaded end of the rod of the first wall sector by a turnbuckle coupling, and the prestress is generated by tightening this coupling. In the construction of each successive sector, the space surrounding the reinforcing rod (within the shielding tube) is filled with grout through the use of hollow reinforcing rods and couplings provided with lateral vent holes. Grout is injected at the projecting end of the reinforcing rod. and flows down the length of the rod and laterally out through the coupling. The flow continues until it emerges from the space surrounding the rod within the shielding tube at the end where the grout is applied. At the closure sector, the grout is injected at an aperture in the turnbuckle coupling in a space defined by a boxedout portion of the form system.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a circular concrete structure cast in successive sectors.

FIG. 2 is a plan view of the structure shown in FIG. 1, on an enlarged scale.

FIG. 3 is a fragmentary section on a horizontal plane of the area indicated at 3-3 in FIG. 2, on an enlarged scale.

FIG. 4 is an enlarged fragmentary section illustrating the application of pre-stress tension (post-tensioning) at the end of a wall sector.

FIG. 5 is a section on a horizontal plane at the junction between successive wall sectors.

FIG. 6 is a section similar to FIG. 5, at the junction of a closure sector of the wall with the initial sector.

FIG. 7 shows the preferred arrangement for placement of the reinforcing rods in the space between the form panels prior to the pouring of the concrete.

FIG. 8 shows the arrangement for shielding the reinforcing rods with a plastic tube.

FIG. 9 shows a modification of the arrangement shown in FIG. 6.

DESCRIPTION OF THE PREFERRED PROCEDURES The wall structure generally indicated at 10 in FIG. 1 is constructed of successively-placed sectors as indicated at 14-21. Referring to FIG. 7, each of the sectors is constructed by the use ofa form system including the spaced panels 22 and 23 reinforced, respectively, by parallel vertical studs 24 and 25. The walers 26-27 bear against the outer surfaces of the studs 24, and the walers 28-29 against the outer surfaces of the studs 25. Bolts referred to commonly as she-bolts as shown at 30 and 31 traverse the panels 22 and 23, and are interconnected by the inner tie-rod 32 in threaded engagement with both of the bolts. The pressure of the concrete poured between the panels 22 and 23 is thus placed in opposition, and equalized. When the concrete between the panels 22 and 23 has set, the bolts 30 and 31 are unscrewed ,by the application of a wrench to the end flats 33 and 34, leaving conical recesses in the spaces previously occupied by the ends 35 and 36 of the bolts. Stresses are transferred from the bolts to the walers by adjustable wedges as shown at 37 and 38 which bridge across the walers, and engage forged or broached flats (not shown) at an intermediate point on the bolts.

The form system for constructing the wall sectors includes end panels as shown at 39 in FIG. 7 for defining the end ofthe space between the panels 22 and 23. The end panels are provided with holes for receiving the ends of reinforcing rods as shown at 40. These may be of a type commonly referred to as rebar, having a corrugated periphery as shown in FIG. 6, or the rods may be smooth on the outer surface. In either case, they are preferably hollow. A small-diameter passage as shown at 41 extends throughout the length of these rods. The ends of the rods are exteriorly threaded as shown at 42 and 43 in FIG. 6. The rods are covered by a preferably plastic shielding tube as shown at 44, and this assembly of rod and tube may be supported conveniently on the central tie rods 32 of the tie system. An anti-rotation offset as shown at 45 normally present on these tie rods may be used as a locating point for the reinforcing rod and tube to assure placement at the central portion of the space between the form panels 22 and 23. If the offset 45 is positioned upwardly, it may also be used as a means of placing the reinforcing rods either radially inward or outward from the center ofthe space, as may be desired according to stress conditions.

When the concrete of the initial wall sector 21 has been constructed as previously described, at least the end panels 39 are preferably removed. Bearing plates as shown at 46 and 47 are slipped over the ends of the rod 40, and the nut 48 is run down against a washer (optional), so that all looseness is removed between the nut and the bearing plate 46. At the opposite end of the rod, the projecting threaded end 49 of the rod 40 is connected by a temporary coupling 50 to the piston rod 51 of the hydraulic jack 52. A set of struts as shown at 53 and 54 exposes the coupling 50 and the end 49, so that the base 55 of the jack bears against the bearing plate 47. The central portion of the base 53 is provided with a standard cutout area so that the nut 56 can be run down onto the bearing plate 47 after the pre-stress loading has been applied to the rod 40 by the hydraulic jack 52. The coupling 50 is then disconnected, and the jack removed.

After the pre-stress has been applied, grout is injected at the end 49 by the application of standard fittings, utilizing technique and equipment common in the installation of rock-bolts. Grout is pumped into the central passage 57 of the rod 40 after this passage has been blocked at the opposite end 42 by the insertion of a small peg. The rod 40 associated with the first sector of the wall is provided with the cross-drilled hole 58 just inside the bearing plate 46, and the grout continues down through the passage 57 to this point. From here it moves laterally outward into the space between the rod 40 and the shielding tube 44, and continues back to the opposite end of this tube where it appears around the opening in the bearing plate 47 traversed by the rod 40. The space around the rod at the bearing plate 46 must not provide a substantial opening for the emergence of grout. After this grout has set, this particular pour sector of wall may be considered as complete.

The formation of the adjacent sector 20 of the wall begins with the erection and securing of the forms as shown in FIG. 7, with the end 59 of the first sector defining one end of the space between the form panels. and thus replacing one of the end panels 39. When the cross-tie systems have been installed, the hollow reinforcing rod 59 is placed in position, and connected to the end 49 of the rod 40 by the coupling 60. (Refer to FIG. 5.) This can be accomplished either by threading the coupling 60 down onto the end 49 beyond its normal position, and then back-rotating it onto the threaded end of the rod 59, or by placing the coupling 60 initially in its correct axial position with respect to the end 49, and then rotating the rod 59 into the correct engagement with the coupling. In either case, care should be taken to assure that the ends of the rod do not obstruct the lateral ports 61 and 62 ofthe coupling. which are provided by a cross-drilled hole. The shielding tube 63 is then slipped axially into the position shown in FIG. 5, in which the coupling 60 is covered, and the end of the tube 63 is fairly well blocked by the presence of the washer 64 and the nut 56. The concrete is then poured to form the wall sector 20, as previously described. When this concrete has set, the end panel of the form system is removed, and a bearing plate slipped over the projecting end of the rod 59, in the position of the plate 47in FIG. 4. Note that a bearing plate at the opposite end ofthe rod is unnecessary. The jack is then applied to the rod 59 to generate the necessary tension, which is secured by running a nut down onto the bearing plate as before.

When the tensioning operation has been completed, grout is injected at the projecting end of the rod 59 as it was in the end of the rod 49. In this case, however, the grout proceeds through the central passage to the coupling 60, where it emerges through the lateral ports 61 and 62 which take over the function of the crossdrilled hole 58in the rod 40. It is usually somewhat eas ier to manufacture the couplings 60 with the ports 61 and 62 than it is to provide the cross-drilling operation in the reinforcing rods, and the latter is therefore usually restricted to the rods of the initial sector, where passage out through a coupling is not possible. Injection continues until the group emerges at the bearing plate adjacent the end of the rod where the grout is being injected. When this grout sets, the second wall sector may be considered as completed. This procedure is continued around until the next step is the formation of the closure sector 14.

The forms are erected for the closure sector, with the ends of the space between the panels defined by the opposite ends of the last-formed sector and the first sector. In otherwords, the forms are simply clamped to the inner and outer faces of the sectors, without the necessity of end-plates 39. When the cross-tie systems have been installed, the reinforcing bar for the closure sector is installed as previously described. The coupling at the closure end of the reinforcing rod for the closure sector is different from the couplings 60. The threaded end 43 of the rod of the closure sector is of opposite hand to that of the threaded end 42 of the first sector, and the closure coupling 64 is thus able to function as a turnbuckle. In the installation of the last rod, it will usually be advisable to first engage the turnbuckle coupling 64 with at least three or four threads of engagement, and then engage the opposite coupling by back-rotation to a degree sufficient for the transfer of stresses. The space around the turnbuckle coupling 64 and the ends 42 and 43 of the reinforcing rods is boxed out by conventional form procedures to define and access opening that will remain free of the concrete poured to form the closure wall sector. Conceivably, this opening could have been formed in the initial sector. The concrete is then poured, and permitted to set. A wrench may then be applied to the turnbuckle coupling 64 to a predetermined degree of torque, resulting in the application of the necessary pre-stress. The tightening of the turnbuckle coupling completes a peripherallycontinuous tension system including the rods and cou plings, with the bearing plates now being of secondary importance. The presence of the grout prevents the rods from shifting position to release ring tension. The turnbuckle coupling 64 is provided with a threaded lateral opening centrally along its length for receiving the grout-injection fitting 65. This fitting is installed after the turnbuckle has been appropriately tightened. The injection of grout at this point causes it to flow via the central passage of the rod 66, and back through the space between this rod and its shielding tube 67 via the lateral ports in the coupling at the opposite end of the rod 66 from that shown in FIG. 6.

FIG. 9 shows an alternative arrangement to that shown in FIG. 6. The hollow rod 68 ofa first wall sector terminates short of the end of the sector, and is connected to the short length of solid rod 69 (threaded at both ends) by the coupling 70 similar to the coupling 60 in FIG. 5. The lateral ports 71 and 72 serve the function of the hole 58 in FIG. 6. The FIG. 9 arrangement removes the need for the inconvenient cross-drilling operation, and maintains the full strength of the rod. It may also be noted in passing that the first wall sector can be grouted by the use of a tube traversing a convenient hole in one of the bearing plates, and communieating with the space between the rod and the shielding tube. This practice is comparable to so-called upgrouting of rock bolts extending upwardly from the point of emergence. This practice is not considered as efficient as either of the above procedures in the present case.

The components of the form system can be stripped at any convenient time, and the removal of the components defining the boxed-out space shown in FIG. 6 will permit this space to be filled with either grout or concrete, as may be preferred. The sequence of wall sectors is then completed.

I claim:

1. A method of constructing a circular pre-stressed reinforced concrete wall, said method including placement of spaced form sections and pouring concrete between said spaced sections, wherein the improvement comprises:

placing spaced form sections including end panels to form a first sector of a circular wall;

placing a shielding tube around reinforcing rod means having threaded ends, and placing said tube and rod means peripherally in the space between said form sections, with said ends projecting from said end panels;

pouring concrete between said form sections including submerging said tube and rod means, and permitting said concrete to set; exposing at least part of the ends. of said set concrete, and applying bearing plates over said rod means ends, and nut means to said threaded ends;

applying tension to said rod means between said plates, and securing said nut means;

placing form sections to form an adjacent sector of said wall with an end of said set concrete of said first sector defining one end of the space between said form sections, the opposite end of said space being defined by an end panel;

placing a shielding tube around reinforcing rod means having threaded ends, and placing said tube and rod means peripherally in the space between said form sections, and coupling one end of said rod means of said adjacent sector to said rod means of said first sector, the opposite end of said adjacent sector rod means projecting from said opposite end panel;

pouring concrete in said space: between said form sections submerging said tube, rod means and cou pling, and permitting said latter concrete to set to form said adjacent sector;

exposing at least part of the end of said set concrete of said adjacent sector defined by said opposite end panel and applying a bearing plate over the end of said rod means projecting from said opposite end and nut means to said latter threaded end; applying tension to said latter rod means;

repeating the steps for constructing said adjacent sector to form successive adjacent sectors of said wall; placing form sections to form a closure sector of said wall, the space between said form sections being defined by the ends of the set concrete of said first sector and the last of said adjacent sectors; placing a shielding tube around reinforcing rod means having threaded, one of said threaded ends being of opposite hand to the threaded end of said rod means projecting from said first sector, placing said latter tube and rod means in said space between said form sections, coupling said latter rod means to the rod means projecting from said last adjacent sector, and applying a turnbuckle coupling connecting said rod means of said first sector and the rod means of said closure sector, and boxing out a space between said form sections surrounding said turnbuckle coupling, said space providing access from the exterior of said wall; pouring concrete between said form sections, including submerging said tube and. rod means and permitting said concrete to set to form said closure sector; and

tightening said turnbuckle coupling to apply tension to the rod means of said closure sector.

2. A method as defined in claim 1, whereinsaid rod means is hollow, and the rod means of said first sector is provided with a transverse hole adjacent one end thereof, said couplings having lateral apertures, and additionally including the steps of injecting grout via said hollow rod means after the application of tension thereto, said grouting being injected in said rod means of said closure sector at said turnbuckle aperture, and in said rod means of said first sector at the end thereof opposite from said transverse hole.

3. A method as defined in claim 1, additionally including the steps of securing said form sections with tie systems traversing the space between said sections, and at least partially supporting said tubes and rod means on said tie systems.

4. A method as defined in claim 3, wherein said systems have a central offset, and said tubes and rod means are engaged with said offset to locate said rod means laterally in the space between said form sections.

5. A method as defined in claim 1, wherein the rod means of said adjacent and closure sectors are hollow, and the rod means of said first sector is hollow over a major portion of its length, and includes a coupling connecting said major portion to a solid rod threaded at its opposite ends, said couplings having lateral apertures, and additionally including the steps of injecting grout via at least certain of said rod means after the application of tension thereto, said grouting being injected in said rod means of said closure sector at said turnbuckle aperture.

6. A method as defined in claim 5, where said grouting is continued in each sector until grout appears at the end of said shielding tube adjacent the point of injection of said grout.

7. A method as defined in claim 6, additionally including the steps of stripping said form sections and end panels from said set concrete as each of said sectors is constructed, and also stripping said boxed-out portion and filling said access space with cementitious material.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3, 869, 530

DATED March 4, 1975 INVENTOR(S): Chester I, Wi||iqms It is certified that error appears in the above dentified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 65 group should be grout Column 5, line 24 and should be on Signed and sealed this 24th day of June 1975.

(SEAL) Attest:

C. i-iARS azkLL DAKN Commissioner of atents and Trademarks RUTH C. f-IASON Attesting Officer 

1. A method of constructing a circular pre-stressed reinforced concrete wall, said method including placement of spaced form sections and pouring concrete between said spaced sections, wherein the improvement comprises: placing spaced form sections including end panels to form a first sector of a circular wall; placing a shielding tube around reinforcing rod means having threaded ends, and placing said tube and rod means peripherally in the space between said form sections, with said ends projecting from said end panels; pouring concrete between said form sections including submerging said tube and rod means, and permitting said concrete to set; exposing at least part of the ends of said set concrete, and applying bearing plates over said rod means ends, and nut means to said threaded ends; applying tension to said rod means between said plates, and securing said nut means; placing form sections to form an adjacent sector of said wall with an end of said set concrete of said first sector defining one end of the space between said form sections, the opposite end of said space being defined by an end panel; placing a shielding tube around reinforcing rod means having threaded ends, and placing said tube and rod means peripherally in the space between said form sections, and coupling one end of said rod means of said adjacent sector to said rod means of said first sector, the opposite end of said adjacent sector rod means projecting from said opposite end panel; pouring concrete in said space between said form sections submerging said tube, rod means and coupling, and permitting said latter concrete to set to form said adjacent sector; exposing at least part of the end of said set concrete of said adjacent sector defined by said opposite end panel and applying a bearing plate over the end of said rod means projecting from said opposite end and nut means to said latter threaded end; applying tension to said latter rod means; repeating the steps for constructing said adjacent sector to form successive adjacent sectors of said wall; placing form sections to form a closure sector of said wall, the space between said form sections being defined by the ends of the set concrete of said first sector and the last of said adjacent sectors; placing a shielding tube around reinforcing rod means having threaded, one of said threaded ends being of opposite hand to the threaded end of said rod means projecting from said first sector, placing said latter tube and rod means in said space between said form sections, coupling said latter rod means to the rod means projecting from said last adjacent sector, and applying a turnbuckle coupling connecting said rod means of said first sector and the rod means of said closure sector, and boxing out a space between said form sections surrounding said turnbuckle coupling, said space providing access from the exterior of said wall; pouring concrete between said form sections, including submerging said tube and rod means and permitting said concrete to set to form said closure sector; and tightening said turnbuckle coupling to apply tension to the rod means of said closure sector.
 2. A method as defined in claim 1, wherein said rod means is hollow, and the rod means of said first sector is provided with a transverse hole adjacent one end thereof, said couplings having lateral apertures, and additionally including the steps of injecting grout via said hollow rod means after the application of tension thereto, said grouting being injected in said rod means of said closure sector at said turnbuckle aperture, and in said rod means of said first sector at the end thereof opposite from said transverse hole.
 3. A method as defined in claim 1, additionally including the steps of securing said form sections with tie systems traversing the space between said sections, and at least partially supporting said tubes and rod means on said tie systems.
 4. A method as defined in claim 3, wherein said systems have a central offset, and said tubes and rod means are engaged with said offset to locate said rod means laterally in the space between said form sections.
 5. A method as defined in claim 1, wherein the rod means of said adjacent and closure sectors are hollow, and the rod means of said first sector is hollow over a major portion of its length, and includes a coupling connecting said major portion to a solid rod threaded at its opposite ends, said couplings having lateral apertures, and additionally including the steps of injecting grout via at least certain of said rod means after the application of tension thereto, said grouting being injected in said rod means of said closure sector at said turnbuckle aperture.
 6. A method as defined in claim 5, where said grouting is continued in each sector until grout appears at the end of said shielding tube adjacent the point of injection of said grout.
 7. A method as defined in claim 6, additionally including the steps of stripping said form sections and end panels from said set concrete as each of said sectors is constructed, and also stripping said boxed-out portion and filling said access space with cementitious material. 